Exhaust Downpipe

[935racer]

oh God, dont get me started on 034, at the shop i work at, we have a audi coupe quattro were doing a ***-ton to, and its a track car, the owner found out 034 was selling brand new "quick ratio" steering racks for his car, so he dropped the $500 or w/e it was for it, it comes in the mail, and is nothing more than a USED audi 4 cyl. rack that was wire-wheeled to take the greese and rust off and still looked like hell!!!!

Oh man I know, I've been doing so much audi fab lately, all the 034 downpipes don't fit, the last two I tried installing on a urS4 and a urS6 didn't even bolt up! They were $600USD a piece, the welding was crap, the materials were crap, I fixed one of them to make it fit, it cracked on one of the 034 welds two weeks later, the other customer was so pissed I don't even know what he did with it, but I made him a custom one.

And their software... man just go standalone guys.

[Darth Garry]

Well, I definately would go for the 3" pipe next time around, which hopefully won't be too far down the road from now.  I don't have any doubt which one is truly the superior product.  Heck, I might buy one sooner and sell the TT one before it cracks!

Garry

[myke_w]

IIRC, the outlet on the k14, k24 and garret turbo isnt even 3", more like 2.25" So why the 3" downpipe craze?

As long as the pipe is at least as big as the outlet, it should spool as fast as it ever will, right? bigger is just excessive isn't it?

The picture in my mind is this - garden hose on full blast  hooked up to a fire hose..  

In other words, everything is limited by the size of the initial outlet, correct?

help me see the logic.

myke_w

[Turbinepowered]

I think, but don't quote me on this as "THE WORD," but I think that it has to do with setting up the pressure differential across the restriction.

I mean, the manifold pipes and valve openings aren't two and a quarter inches in diameter, but fitting an exhaust pipe up to that size helps anyway, right? Free flowing and all that. What I think happens, is the bigger your pipe after the restriction, the lower the pressure on that side.

As pressure differential increases across a restriction, flow increases. So if you're going for flow, you want as big a pressure differential across that restriction as possible, ideally without increasing any of the pressures involved (as that would mean you're working the engine harder just to push gases out).

[saurkraut]

Ideally, the pipe needs to be significantly bigger to change the spiral flow coming out of the turbo into turbulent flow.  Turbulant flow is allot faster than spiral flow.

On the 1.6TDs: 2.5 flows better than the original exhaust, and its a quantum leap.  3" flows better than 2.5", and its noticable, but not a quantum leap.

[935racer]

IIRC, the outlet on the k14, k24 and garret turbo isnt even 3", more like 2.25" So why the 3" downpipe craze?

As long as the pipe is at least as big as the outlet, it should spool as fast as it ever will, right? bigger is just excessive isn't it?

The picture in my mind is this - garden hose on full blast  hooked up to a fire hose..  

In other words, everything is limited by the size of the initial outlet, correct?

help me see the logic.

myke_w

The k14,k24,t2,and t3 turbines are all 2.25" outlets.

The reason the downpipe needs to be larger is because the exhaust gas is under pressure and it is EXPANDING. The water in the hose is not. Going to a larger size allows the exhaust to escape/expand faster, which: reduces pressure post turbo (allowing turbo to spool up sooner), less pressure in this situation also means less heat, both egts and in just plain cooking your turbo which heats up the journal area and super heats your oil.

Anyone have a picture from Corkey Bell's turbo book showing the swirl change post turbine with the use of a transition?

[hillfolk'r]

Ideally, the pipe needs to be significantly bigger to change the spiral flow coming out of the turbo into turbulent flow.  Turbulant flow is allot faster than spiral flow.

On the 1.6TDs: 2.5 flows better than the original exhaust, and its a quantum leap.  3" flows better than 2.5", and its noticable, but not a quantum leap.

vortex generators,my man ,vortex generators
vortex generators will change the spiral flow to turbulent,for improved flow
 :wink:
http://x-jets.com